Routing vacuum lines without EGR-system

[timachone]

Hi guys,

while restoring the engine bay here and there and fiddling with my Pertronix I came over this:

My dual diaphragm vacuum distributor seems to not have been routed right with the vacuum lines. The "P"-line goes right to the carb's vacuum port but the "S"-line goes to a distributor vacuum control valve and from there to nowhere - it is capped of. That does not make any sense to me...

I have the complete original EGR and vacuum assembly removed and I do not have any of the original parts as a spare. What I have installed on my original q-code block is the following:

- an 1970 Autolite dizzy with a dual diaphragm vaccum unit (Pertronix I inside)

- an 1970 Autolite 4300 D carb with one vacuum port on the front

- a distributor vacuum control valve with two ports instead of three on the coolant thermostat side in the block in the front near the heater hoses. It was originally for the EGR-system.

- the vacuum-tree on my intake manifold (Offenhauser aluminium) on the back. The big line goes to the power break booster.

How to rout now the two lines from the dizzys diaphragm vacuum unit correctly without all the original EGR and something?

I have no AC - only power steering, power breaks, manual transmission and a big fuel tank

Originally it was like this

http://www.mustangbarn.com/images/vacs/73%203-15A.gif

Should I connect it like this (I do not have the 3-ports control valve respectively the "filter" pin)

http://www.allfordmustangs.com/forums/attachments/classic-tech/106707d1281142812-1968-289-mustang-massive-vacuum-leak-but-i-cant-hear-vacuumhose.jpg

or completely bypass the original EGR vacuum control valve like this

http://repairguide.autozone.com/znetrgs/repair_guide_content/en_us/images/0996b43f/80/22/64/a3/large/0996b43f802264a3.gif

I don't know now what the 2-port vacuum control valve could do for my performance without the EGR-system...

Is there an easy method to test the dual diaphragm unit on the dizzy of it's correct function concerning the diaphragms?

Any help would be appreciated...

Tim

 

[Paul of MO]

The side port on a 2 port dizy is for a overheat controlled retard system that was part of the emissions system. It was more of an engine protection system.

A temp controlled vacuum switch opened when water temp got high and applied suction to the back side of the distributor diaphragm reducing the amount of advance when accelerating. This protected the engine from pinging and melting the pistons.

There were 2 vacuum temp switches - one for the EGR under the carb for cold starts - and the other for the distributor. They are separate from each other and open at much different temps. Get them mixed up and your car will run OK cold and then dog out once it is warmed up. Get them mixed up the other way and your EGR will never operate correctly and your car will run like crap. Auto parts store are notorious for giving out the wrong one.

I never hook these up because I will not keep driving if my engine is overheating and I like a nice clean uncluttered engine compartment.

I have a whole box of them collecting dust right now.

One vac line to the distributor works quite well.

- Paul

 

[timachone]

Hi Paul,

thank you for bringing some more light into the vacuum darkness

So you would only route the outer port of the dizzy to the carb and block the inner one with a cap? No routing of the inner side port to the intake vacuum? So it will function like the ones with only one diaphragm outlet?

Tim

 

[Paul of MO]

I just leave the side port open if I keep the factory distributor. I never tested to see if capping it had any effect. I would guess capping it would somewhat slow how fast the ignition advanced when going wide open throttle if anything.

Most often I install an MSD pro billet distributor without a vacuum advance.

That with a MSD 6AL ignition box is pretty much bulletproof for a street car. I can still get jobber pricing direct from MSD and they build a great product.

And yes, I just run a single vac line from the front of the distributor to the lowest port (for manifold vacuum) on the carb base plate. A port on the intake vacuum tree will also work but not as well.

- Paul

 

[timachone]

Thanks, Paul!

Tim

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